Materials technology has had a profound impact on the evolution of human civilization. In the 21st century, people are developing smart materials and smart sensors. The class of engineered smart materials based on piezoelectric materials, organic polymers and silicon are useful in micro electro mechanical (MEM) or microelectronic sensors. The engineered smart materials and sensors have the potential for making a major impact on the design and application of structural components and engineering structures, known as “smart structures.”
Smart structures are designed to react to the surrounding environment by use of integrated sensors and actuators within the form. Such structures not only can monitor the status of their functioning but also forewarn about the onset of abnormalities and hence impending failures. The smart sensors made of smart materials are to provide in association with other components like actuators and control systems, the required functional capability so as to react to internal and external environments and achieve adaptability. Examples are: smart planes, smart space ships, smart cars, smart bridges and highways, to mention a few. Thus, the fast developing area of smart structure systems is evolving, and an advanced combination of materials, sensors, actuators, control and processing are blended suitably to achieve the end result.
The development of smart materials and sensors has been challenging for some structures, such as gas turbine engines, space craft and the like, because they operate at extreme conditions of temperature, pressure, fluid (air/gaseous mixture, air/fuel mixture) velocity, and the like.
Direct measurement of hot gas properties at the exit of a gas turbine combustor and inlet of the first row of vanes or nozzles under actual operating conditions is quite difficult, if not impossible, with currently available measurement tools. This information is needed both for real-time monitoring so that operation can be optimized as well as for having accurate data for optimized design of downstream components. Temperatures at that location can be in excess of 1800° K, and the chemical conditions are quite hostile, rendering any off-the-shelf intrusive probe quite useless.
Under operating conditions and for accurate measurements, the shroud around this flow path has to be heavily insulated in order to avoid heat loss (which can additionally increase the radial temperature gradient and adversely affect the temperature profile approaching the vanes). Also, because of space and geometric restrictions, and extreme flow conditions, optical windows (for transmitting and receiving optics) are difficult to implement. Typical optical measurement techniques conventionally used for measuring velocity, turbulence, temperature and species, for example, Laser Doppler Velocimeter (LDV), Particle Image Velocimetry (PIV), Coherent Anti-Stokes Raman Scattering (CARS) and Laser Induced Fluorescence (LIF) cannot readily be used without major modifications. As a result, current turbine design primarily relies on estimated or computed data obtained from Computational Fluid Dynamics' (CFD) simulations, the very basis of which is questionable under present experimental conditions. Yet the flow conditions at the combustor exit are very important for turbine design as they form the inlet boundary conditions for turbine design process.
Spectral measurements may be recorded, for example, using equipment such as a paper tablet, computer, compact disc, digital pen, digital video disc, and the like.
Capability for hot flow path measurements for the purpose of better turbine design is even more important for newer power generation concepts such as clean coal technology and Integrated Gasification Combined Cycle (IGCC) plants. Although these concepts have been around for over a decade, there continues to be a need for additional demonstration plants that can provide the necessary performance data to help in optimal design and selective retrofitting.
Human civilization needs sensors that can be integrated into structures that operate in extreme, harsh and hostile environments.